Leszek Michalak

Ion/molecular reactions as an effect of crossing a highly non-homogeneous effusion molecular beam with an electron beam

Abstract An effusive molecular beam emitted by a cylindrical capillary was ionized by a transverse electron beam which could be displaced perpendicularly and along the capillary axis. This system was the open ion source of a cycloidal mass spectrometer which was used to identify both primary ions, generated by ionizing the molecules by electrons, and secondary ions produced in ion/molecular reactions. Thus, the ionization processes and the ion/molecular reactions that take place were recorded directly, free of effects concerned with walls and slots, which are characteristic for conventional ion sources. Secondary CH + 5 and C 2 H + 5 ions were recorded in the case of a CH 4 beam and H 3 O + ions in case of a H 2 O beam. The ion/molecular reaction areas of the effusion molecular beams were roughly determined by changing the electron beam position relative to the capillary.

Role of the support material on laser desorption/ ionization mass spectra

We report the results of experimental studies on the effects of sample supports in laser desorption/ionization mass spectrometry (LDI-MS). LDI time-of-flight (TOF) mass spectra obtained for C(60) and insulin samples deposited onto standard stainless steel substrate and/or onto some non-metallic materials (glass, scotch tape, floppy disc foil, Teflon foil, photocopy film), all recorded under identical, typical experimental conditions, have been compared with regard to their intensity and quality. The LDI investigations show that compared with stainless steel, glass and floppy disc foil sample supports boost (2-3.5 times) ion yields for C(60)(+) and C(60)(-) ions, respectively. The stainless steel and scotch tape sample supports are the best for the mass resolution of positive ions and the formation of (C(60))(n)(-) (n <or= 4) cluster ions, respectively. In the case of detection of insulin by matrix-assisted laser desorption/ionization (MALDI) we did not observe significant differences in sensitivity for the support materials tested. A mechanism of ion formation in the desorption plume is suggested.

Modelling of the molecular beam intensity distribution in the ion source of the mass spectrometer by means of a light beam

Abstract The analogy between a molecular beam and a light beam is presented and the case where a molecular beam in the ion source of the mass spectrometer is crossed by an electron beam is discussed. The transverse intensity distribution of a molecular beam formed by a capillary was compared with the transverse distribution of a light beam formed by a tube lined inside with corrugated aluminium foil with a high reflection coefficient. In the capillary, effusion of gas was observed, and in the tube, “effusion” of light. The transverse intensity distributions of both beams were comparable.

Effusive molecular beam crossed by an electron beam and the optical model of this effect

Abstract By means of a cycloidal mass spectrometer, the intensity of an N2+ ion beam formed by the crossing of an effusive molecular beam generated by capillaries of various lengths, with an electron beam of circular cross-section (cylinder) was examined. The authors see a close analogy between the effusive beam crossed by the electron beam and the effusive light beam crossed by the diffusing glass screen in the form of a cylinder.

Electron impact study of carbon disulphide micro-clusters

Abstract The production of carbon disulphide micro-clusters (CS 2 ) n , n ⩽11, by adiabatic gas expansion of mixture of CS 2 vapour and Ar is studied by using an electron impact ion source and a double focusing sector field mass spectrometer. The appearance potentials for clusters n ⩽9 decreased as n increased but was not a simple function of 1/ n . The appearance pressures of observed clusters showed a slowly increasing dependence on cluster size. Results of measurements of appearance potentials and appearance pressures of selected clusters are described for a range of operating conditions.

Electron ionization study of ammonia micro-clusters

An electron impact ion source on a double focusing sector field mass spectrometer was used to investigate ammonia micro-clusters produced by the adiabatic free jet expansion of ammonia gas. The appearance energies for [NH(3)](n)(+), n </= 9, ions have been determined. Results of measurements of appearance pressures of selected clusters are described for a range of operating conditions. An empirical formula describing the ammonia clusters production is proposed. Copyright 2000 John Wiley & Sons, Ltd.

Production of carbon disulphide dimers by an adiabatic gas expansion method

Abstract The production of carbon disulphide dimers by adiabatic gas expansion of a mixture comprised of CS2 vapour and Ar is studied by using an electron impact ion source and a double focusing sector field mass spectrometer. Results of measurements of the generation of (CS2)2+ cluster ions versus the stagnation pressure (0–160 kPa) at several stagnation temperatures (267–300 K) are described. An empirical formula describing the carbon disulphide dimer production is proposed.

Electron ionization of the effusion molecular beam emitted by a rectangular channel and the optical model of this effect

Abstract Based on previous investigations, the authors have measured the intensity of an N2+ ion beam, which was generated by crossing an effusion molecular beam of nitrogen with an electron beam. The molecular beam was emitted both from a flat slit and from a rectangular channel. The dependence of the ion current intensity and the electron beam position in relation to the outlet of the effusion hole has been examined. The authors have also demonstrated an optical model of the examined effect.

Calculation of the number of molecules in an electron beam crossed by a non-homogeneous effusion molecular beam

Calculations of the number of molecules in an electron beam crossed by a non-homogeneous effusion molecular beam generated directly by a cylindrical capillary are presented. The influences of geometrical parameters and the mutual configuration of an effusion capillary and an electron beam on the number of molecules in the electron beam are examined. The theoretical results are compared with results obtained for CH4 and H2O molecular beams ionized by an electron beam in the open ion source of a cycloidal mass spectrometer.

Size-dependent fragmentation of carbon dioxide clusters

A combined nozzle cluster source system and double focusing sector field mass spectrometer were used to study the fragmentation of (CO 2 ) + n cluster ions (n < 22). The ions were generated by electron impact. The relative intensities of the fragment ions are found to be dependent on cluster size. The high abundance of ions (CO 2 ) 4,5 X + and (CO 2 ) 15,16 X + (X = O, CO, O 2 ) indicate pronounced stabilities of these cluster ions.